Acute kidney injury (AKI) affects more than 10 million people worldwide each year with reported mortalities from 15 to 60% in different patient populations. However, methods are lacking to support the early diagnosis of AKI that could lead to early intervention, improved therapy, better prognosis, and lower medical costs. For these reasons, the development of early diagnosis tools for AKI is one of the solicited research topics listed by the NIDDK. Neutrophil gelatinase-associated lipocalin (NGAL) is a reliable biomarker for AKI and may also have some predictive uses. We propose to develop a portable device for reliable early detection of AKI at point-of-care. The innovation of our proposal lies in the combination of aptamer technology with microcantilever detection of NGAL, an early marker of AKI [2-4h at the onset of AKI; cutoff ~150 ng/ml]. Aptamers are single stranded DNAs or RNAs that bind their targets avidly and specifically, and are selected in vitro by Systematic Evolution f Ligands by Exponential enrichment (SELEX). For biosensor development, aptamers have many advantages over antibodies, including their smaller size, amenability to chemical synthesis and modifications and adaptability to a broad range of assay formats including a microcantilever detection system. A microcantilever is a beam, often of silicon, that is 1-5 m thick and 500-100 m long and anchored only at one end. The microcantilever bends when its surface stress changes due to the conformation change that occurs upon ligand-receptor (e.g. aptamer-target) interaction on its surface. The differential surface stress between a reference cantilever coated with a scrambled nucleic acid that does not bind the analyte and a sensing cantilever coated with an aptamer that binds the analyte is measured by interferometry. In a phase I study, we isolated several aptamers that bind NGAL and demonstrated the abilities of one of these to sense NGAL when the aptamer is attached to a microcantilever. In this phase II study, we propose the following specific aims: 1) Compare several aptamers for specificity, functionality in the presence of serum proteins, affinity for NGAL, effectiveness in the presence of salt mixtures characteristic of plasma and urine, and compatibility with the microcantilever device, 2) Optimize the best performing aptamers for length, sequence, stability and optimal assay performance in blood and urine, and 3) Optimize the microcantilever device for aptamer sensing (dynamic range of 1-100 nM for detection, signal/noise ratio > 10, covariance < 10%). Miniaturize the microcantilever device to a size equal to or smaller than a shoebox. From these studies, we expect to develop an optimized and reliable aptamer-functionalized microcantilever by which NGAL can be quantified in plasma and urine samples with robust signal/noise ratio, sensitivity, detection limit and dynamic range of measurement. Phase III studies will involve manufacturing and validating the device for monitoring NGAL to detect AKI at point-of-care.